The present invention relates to a prefabricated structure permitting to provide fluid-tight and thermally insulating walls for a lagged confinement structure such as a fluid-tight tank for the storage and/or the transport of a fluid at very low temperature such for example as a liquefied gas or a cryogenic liquid.
One has already described in particular in the document FR-A-2,599,468 in the name of the applicant, a structure constituted by prefabricated elements assembled so as to obtain a hermetic lagged enclosure which may for example contain liquefied methane. This structure of the prior art may be mounted in the hold or double-hold of a merchant ship. The self-supporting rigid bulkheads form an external support for the other elements of the structure. An internal or primary fluid-tight barrier which defines a substantially deformable hermetic vessel provided for containing the fluid is assembled from elements generally of metal inside of the space defined by the external partitions of the support. A thermal insulation system is interposed between the external partitions and the primary barrier. This insulation system comprises at least two layers of insulating and fluid-tight material such as a plastic foam with closed cells formed through juxtaposition of prefabricated plates. Both insulation layers are held like a sandwich by two panels for example of plywood for the distribution of the forces inside of the structure. One panel made fast to the external partition is stuck to a so-called "external" insulation layer whereas the other panel, which is made fast to the internal barrier, is adhered to another so-called "internal" layer. To maintain the fluid-tightness of the structure in case of cracking of the primary barrier, plugs provided in the same type of material as the insulation plates are disposed within the joints between the juxtaposed plates of the external layer and then are respectively covered with a strip hermetically stuck to the external layer and generally comprises a central fluid-tight aluminum foil as well as two layers of glass fibre fabric.
However in the known structures at the level of the joints, only the cover strip ensures the fluid-tightness between the internal and external insulation layers. In fact in case of a leakage through the primary barrier, all the fluid-tightness is based upon this strip, thereby risking to generate a cooling if one of these cover strips ceases to be hermetic.
Moreover since in the known structures the panels for the distribution of the forces are constituted by elements assembled with the assistance of screws or the like extending into the joints of the external insulation layer, one concentrates upon the joints the risks of loss of fluid-tightness.